xitca-http 0.9.1

use std::io;

use crate::{
    body::SizeHint,
    http::header::{CONTENT_LENGTH, HeaderMap},
};

use super::frame::headers;

pub(crate) trait BodySize {
    /// Parse content-length from headers.
    /// Returns `Err(())` if the header is present but malformed (RFC 7540 §8.1.2.6).
    fn from_header(headers: &HeaderMap, is_end_stream: bool) -> Result<Self, ()>
    where
        Self: Sized;

    /// Subtract `len` bytes received in a DATA frame.
    /// Returns `Err(())` if this would underflow (overflow: more data than declared).
    fn dec(&mut self, len: usize) -> io::Result<()>;

    /// Returns `Err` if remaining != 0 at END_STREAM (underflow: less data than declared).
    fn ensure_zero(&self) -> io::Result<()>;
}

impl BodySize for SizeHint {
    fn from_header(headers: &HeaderMap, is_end_stream: bool) -> Result<Self, ()> {
        if is_end_stream {
            Ok(Self::None)
        } else {
            match headers.get(CONTENT_LENGTH) {
                Some(v) => {
                    let s = v.to_str().map_err(|_| ())?;
                    let len = headers::parse_u64(s.as_bytes())?;
                    Ok(Self::Exact(len))
                }
                None => Ok(Self::Unknown),
            }
        }
    }

    /// Subtract `len` bytes received in a DATA frame.
    /// Returns `Err(())` if this would underflow (overflow: more data than declared).
    fn dec(&mut self, len: usize) -> io::Result<()> {
        match self {
            Self::Unknown => Ok(()),
            Self::None => Err(io::Error::new(io::ErrorKind::InvalidData, "content-length exceeded")),
            Self::Exact(rem) => {
                *rem = rem
                    .checked_sub(len as u64)
                    .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, "content-length exceeded"))?;
                Ok(())
            }
        }
    }

    /// Returns `Err` if remaining != 0 at END_STREAM (underflow: less data than declared).
    fn ensure_zero(&self) -> io::Result<()> {
        match self {
            Self::Unknown | Self::None | Self::Exact(0) => Ok(()),
            Self::Exact(_) => Err(io::Error::new(io::ErrorKind::InvalidData, "content-length underflow")),
        }
    }
}